The present invention is directed to a mineral polymer composition which is employed for the making of cast or molded products at room temperatures, or temperatures generally up to 248.degree. F., where the composition has attained sufficient strength to be demolded within 90 minutes of casting or molding. These high early-strength compositions are obtained by the blending of a mineral geopolymer, referred to as a polysialate, blast furnace slag, obtained from the making of iron in a blast furnace and possibly, an inert filler.
The mineral geopolymers are called polysialates, and have the following empirical formula: EQU M.sub.n [--(Si--O.sub.2).sub.z --Al--O.sub.2 --].sub.n,wH.sub.2 O
wherein "z" is 1, 2 or 3; "M" is a monovalent cation such as potassium or sodium, and "n" is the degree of polycondensation. Where "z" is 1, the mineral geopolymer has the formula: ##STR1## and is called polysialate or PS for short, and is of the K-PS polymer compound type when "M" is potassium. Where "z" is 2, the mineral geopolymer has the formula: ##STR2## and is called polysialatesiloxo or PSS for short. When "M" is sodium or a mixture of sodium and potassium, the geopolymer is called (sodium, potassium)polysialatesiloxo or NaKPSS. The chemical formula of NaKPSS may be written as: ##STR3##
The method for making NaKPSS or KPS is described in U.S. Pat. No. 4,349,386 and U.S. application Ser. No. 377,204. It comprises preparing a sodium silico-aluminate/potassium silico-aluminate water mixture where the composition of the reactant mixture, in terms of oxide-mole ratios, falls within the ranges shown in Table A below.
TABLE A ______________________________________ Oxide-Mole Ratios of the Reactant Mixture ______________________________________ M.sub.2 O/SiO.sub.2 0.20 to 0.48 SiO.sub.2 /Al.sub.2 O.sub.3 3.3 to 4.5 H.sub.2 O/M.sub.2 O 10.0 to 25.0 M.sub.2 O/Al.sub.2 O.sub.3 0.8 to 1.6 ______________________________________
where M.sub.2 O represents either Na.sub.2 O, or K.sub.2 O or the mixture (Na.sub.2 O,K.sub.2 O).
The usual method for preparing this mixture comprises dissolving in water an alumino-silicate oxide, alkali, and a colloidal silica sol or alkali polysilicate. The alumino-silicate oxide (Si.sub.2 O.sub.5,Al.sub.2 O.sub.2).sub.n may be prepared from a polyhydroxy-alumino-silicate having the formula (Si.sub.2 O.sub.5,Al.sub.2 (OH).sub.4).sub.n, where the aluminum cation is in the octahedral state and is in six-fold coordination. The polyhydroxy-alumino-silicate is calcined and dehydroxylated at, say 1112.degree. F. to 1472.degree. F. The resulting alumino-silicate oxide has the aluminum cation in four-fold coordination and in a tetrahedral position.
Various polyhydroxy-alumino-silicates may be used as the starting material for the preparation of alumino-silicate oxide, including minerals having basal spacings of about seven Angstroms and having at least one aluminum cation located in the octahedral layers. Examples are alushite, carnat, china clay, lithomarge, neokaolin, parakaolinite, pholenite, endellite, glossecolite, halloysite, milanite, berthiernine, fraignotite, grovenite, amesite, and chamoisite.
The quantities of the reactants, namely colloidal silica sol and/or polysilicate, and strong alkalis such as sodium hydroxide and potassium hydroxide, fall in the ranges shown in Table A.
After aging, the mineral mixture may be used alone, or may be mixed with inorganic or organic additives or fillers. The mixture may be used as a binder or a mineral cement for organic or mineral particles or fibers. The mixture is cast, poured or squeezed into a mold and heated to a temperature up to about 467.degree. F. but preferably to a temperature in the range of about 140.degree. F. to about 203.degree. F. When polycondensation is complete, the solids are separated from the mold and dried at a temperature in the range of about 140.degree. F. to about 212.degree. F.
Polycondensation and heating times are a function of the temperature and the heating process used. At an ambient temperature such as 77.degree. F., polycondensation requires more than 15 hours. At 122.degree. F., polycondensation requires about four hours; at 185.degree. F., about 1.5 hours; and at 203.degree. F., about 0.5 hours. These times may differ and are often shorter when other heating techniques are used. Such other techniques include high frequency, microwave, Joule effect, or electrical wires within the reactant mixture itself. Because the reactant mixtures are polyelectrolytes, these heating techniques effect polycondensation and drying very rapidly.
There is a need for a cement which has the high setting and very low volume change characteristics normal for polysialate geopolymers, but which has very early high compressive strengths. This need is particularly acute in the prestress and precast concrete industry. Considerable savings result from the required strength being obtained at early ages so that construction can continue and there is a more rapid reuse of molds. There is also a need for such a very early high-strength cement having the high setting characteristics of polysialate geopolymers in patching or resurfacing highways and airport runways or in any operation where early form removal is desired.
While there have been proposals in the past for a cement having early high compressive strength, none of them have had the early compressive strengths required; that is, cement having a compressive strength better than 1,000 psi by 1 hour at 150.degree. F. and 6,000 psi by 4 hours at 150.degree. F. when tested in a standard 1 to 2.75 by weight cement-sand mortar, and having the high setting and very low volume change characteristics that are normal for, and are typical of, polysialate geopolymers.
The best early high-strength Portland Cement described in U.S. Pat. No. 4,160,674 is made from a Portland Cement having substantially all of its particles of about 20 microns and smaller. This fine and expensive cement type "Incor" had a compressive strength of 3,000 psi in 4 hours at a temperature of 150.degree. F.
The second required component of the high early-strength composition of the present invention is a ground blast furnace slag. Part of the steel-making process is in the reduction of iron ore to pig iron in a blast furnace. A by-product of the iron-making operation is blast furnace slag, the material resulting from the purification of iron ore into pig iron. Blast furnace slags contain, in addition to the lime and magnesia added to the blast furnace as fluxing material, the impurities previously contained in the iron ore, usually silica, alumina, and minor amounts of other compounds.
The ground blast furnace slag employed is a latent hydraulic product which can be activated by suitable activators. Without an activation, the development of the strength of the slag is extremely slow. It is also known that the development of the slag necessitates a pH higher than or equal to 12. The best activators are then Portland Cement, clinker, Ca(OH).sub.2, NaOH, KOH, and waterglass. The 7 day compressive strengths of activated slags with different alkali activators are given in the paper presented by J. Metso and E. Kapans, "Activation of Blast Furnace Slag by Some Inorganic Materials", at the CANMET/ACI First International Conference on the Use of Fly Ash, Silica Fume, Slag and Other Mineral By-products in Concrete", July 31-August, 1983, Montebello, Quebec, Canada. An addition of 4% by weight of NaOH gave a compressive 7 day strength of 12 to 20 MPa (1740 to 2900 psi), and a compressive 28 day strength of 22 MPa (3190) psi.
The addition of ground blast furnace slag to the polysialate geopolymers accelerates the setting time, and improves compressive strength.